Disable input some symbols to JTextField

Question

How can I disable input of any symbol except digits to JTextField?

Answer 1

Just consume all chars that is not a digit like this:

public static void main(String[] args) {
    JFrame frame = new JFrame("Test");

    frame.add(new JTextField() {{
        addKeyListener(new KeyAdapter() {
            public void keyTyped(KeyEvent e) {
                if (!Character.isDigit(e.getKeyChar()))
                    e.consume();
            }
        });
    }});

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 300);
    frame.setVisible(true);
}